Moulding device for the production of containers in thermoplastic material

ABSTRACT

A molding device for the production of containers in thermoplastic material by blowing or blow-drawing, including a mold with two mold halves mutually mobile and provided with a locking device with first and second lock elements, in the form of catches, extending over the whole height of the respective mold halves and a projecting wing on one mold half, including a rotation surface on which a mobile piece is applied over the whole height thereof which includes the second lock element, such that, on blowing, the forces are taken by said mobile piece over the height of the mold by means of the rotation surface.

FIELD OF THE INVENTION

The present invention relates in general to the field of molding devicesfor blow-molding or stretch-blow-molding containers from heatedthermoplastic preforms.

More specifically, the invention relates to improvements made to thoseof these devices that comprise at least one mold comprising at least twohalf-molds that can be moved with respect to each other between an openposition in which they are parted from one another and a closed positionin which they are firmly pressed against one another via collaboratingrespective bearing faces defining a parting line, locking means beingprovided to lock the two half-molds in the closed position, whichlocking means comprising on at least one side of the mold, a first lockelement in the form of a hook secured fixedly to the first half-moldalong the edge of the bearing face thereof, a second lock element in theform of a hook inverted with respect to the previous one and mountedsuch that it can pivot, on a rotation surface, on the second half-mold,and actuating means functionally associated with said second lockelement in such a way as to move the latter transversely between alocked position in which it is engaged with the first lock element tolock the two half-molds in the closed position and an unlocked positionin which it is disengaged from the first lock element to release the twohalf-molds that can then be parted from one another.

DESCRIPTION OF THE PRIOR ART

Document FR-A-2 646 802 discloses means for locking two half-molds inthe closed position which means comprise a plurality of coupling fingerssupported one above the other, coaxially, by a first half-mold and ableto be moved parallel to the axis of the mold to engage in a plurality ofrespective accommodating slots supported by the second half-mold.

Such locking means are satisfactory and are currently in commonplace usein molding devices of the “hinged” mold type.

However, these locking means do have several significant disadvantages.

One disadvantage lies in the fact that the fingers and accommodatingslots are supported in cantilever fashion by the first and secondhalf-molds respectively. As the blowing pressure (for example typicallyof the order of 40×10⁵ Pa) is applied, the supports of these fingers andaccommodating slots, which project radially, are subjected to a forcesubstantially tangential to the periphery of the mold. To prevent themfrom deforming or pulling out, these supports need to be solidly formed,and this increases the weight of the half-molds and also their cost.

Another disadvantage lies in the cantilevered structure of each finger,the base of which is set into a radially projecting support secured toone half-mold whereas, in the locked position, the free end of thefinger is held in a corresponding accommodating slot of a radiallyprojecting support secured to the other half-mold. Under the blowingforce, each finger is subjected to a bending/shear stress which, onceagain, entails that each finger be solidly formed, making it heavy andexpensive.

All these requirements lead to locking means that project appreciablyfrom the periphery of the mold whereas, in installations comprising agreat many molds and operating at high speed (rotary molding devices ofthe carousel type), the space available is very restricted. Furthermore,these locking means are heavy and increase the inertia of thehalf-molds, something which is detrimental to installations operating athigh speed.

Finally, it must be emphasized that the method of locking/unlockingthrough the axial movement of a plurality of superposed (“in line”)fingers entails relatively long travels so that the portion of eachfinger engaged in its corresponding slot is long enough and affordsappropriate mechanical strength: it is therefore possible to provideonly a restricted number of fingers and slots, spaced axially apart byan appreciable distance. This then finally results in a non-uniformdistribution of the forces over the height of the mold.

SUMMARY OF THE INVENTION

There is therefore a remaining need for molds with a simplified, lessbulky, less heavy, simpler and less expensive structure, this need beingfelt all the more keenly as higher production rates are being sought,entailing mechanisms that work more quickly with lower inertia.

For these reasons, the invention proposes a molding device as mentionedin the preamble which, being arranged in accordance with the invention,is characterized by the following combination of arrangements:

-   -   the first and second hook-shaped lock elements extend        respectively over the entire height of the first and second        half-molds,    -   the second half-mold has, along the edge of its bearing face and        over at least most of its height, a radially projecting flange        shaped, on its face facing away from the bearing face, as an arc        of a circle and able to constitute a convex rotation surface,        and    -   said second lock element belongs to one end of a moving part        provided with a transverse projecting flange defining a bearing        surface in the shape of an arc of a circle facing toward the        second hook-shaped lock element and able to bear continuously        over the entire height of said rotation surface of the second        lock element.

Admittedly, locking means for molding devices that employ hook-shapedlock elements are already known, particularly from document U.S. Pat.No. 3,825,396. However, in that known arrangement, the hook-shaped lockelements are not distributed over the entire height of the mold whichmeans that the top and bottom parts of the mold are not sufficientlyfirmly held. What is more, the hook-shaped lock element articulated torotate on one of the two half-molds is supported by a spindle,conventionally passing through devises belonging to the lock element andto the half-mold. Upon blowing, this spindle is subjected to very highshear and possibly bending forces, which means that it needs to be sizedaccordingly and therefore has a large diameter and a high mass.

By contrast, by virtue of the structure proposed according to theinvention, when the closed and locked mold is subjected to the blowingpressure, the force exerted on the second half-mold is reacted by saidmoving part, substantially continuously over most of its height.Furthermore, the rotational travel of the moving part and of the secondlock element is very short, which shortens the locking/unlocking timeand therefore makes it possible to envisage an evolution in theoperating rate. The moving part with the second lock element has reduceddimensions and reduced mass, especially since, in certain exemplaryembodiments, it can be manufactured at least partially in light metal(aluminum) which means that the inertia of the moving components is low.Finally, the number of component parts is reduced and the structure ofsuch locking means is simple, which means that the costs of manufacturecan be lowered.

The devices according to the invention, although their potentialapplications are generalized, may find a quite particularly preferredapplication when the mold is of the hinged type with the two half-moldsarticulated to one another in terms of rotation on a shaft substantiallyparallel to one side of the parting line, in which case said lockingmeans are provided on the opposite side of the two half-molds to saidshaft. In particular, in molding devices in which each half-moldcomprises a shell holder to which there is internally fixed a shellequipped with a molding half-cavity the parting line being defined bythe two shells pressed together when the mold is in the closed position,provision is then made for the locking means to be supported by the twoshell-holders.

In one preferred embodiment which simplifies manufacture, said face ofthe protruding flange of the second half-mold which faces away from theedge of the bearing face is hollowed out in the shape of an arc of acircle and houses a rotation spindle the free surface of whichconstitutes said rotation surface.

As a preference, the rotation spindle of the moving part supporting thesecond lock element is supported by a small number of hollowed-outdevises secured to the second half-mold; as a greater preference, inthis case, the devises are two in number, distant from one another and,in particular, situated near the respective ends of the spindle, andbear no closure force because they are there merely to support themoving part on the corresponding half-mold.

In another preferred exemplary embodiment, the rotation spindle of themoving part supporting the second lock element has a height appreciablygreater than that of the second lock element and its two ends areengaged in two respective cups, secured to the second mold, whereby themoving part supporting the second lock element bears over practicallythe entirety of its height against the rotation spindle.

The first and second hook-shaped lock elements may, depending on thecircumstances, be embodied in various ways. It is possible in particularto envisage for the first and second hook-shaped lock elements to extendcontinuously over their entire height, the two lock elements then beingin the form of solid mold parts or portions. However, for example, withthe desire to lighten the moving parts and reduce inertia, it ispossible to envisage for at least the second hook-shaped lock element toextend discontinuously over its entire height and to comprise amultiplicity of hooks separated from one another and distributed overits entire height, the first hook-shaped lock element also possiblybeing able to be produced in this form.

Furthermore, it is highly advantageous for the rotation spindle to bearranged in the form of an eccentric spindle and for pivot control meansto be associated with it,

whereby the spindle is able to occupy two angular positions with respectto the moving part, namely a first position for which the moving partbears against the part of the spindle that has a minimum radius and canbe made to move toward its locked position or toward its unlockedposition and a second position for which the moving part bears against apart of the spindle that has a radius greater than the minimum radiusand is immobilized in the locked position being subjected to tractionbetween the first and second mutually-engaged lock elements and therotation spindle.

The provisions according to the invention seem to find a particularlyadvantageous application, because of the space savings they afford andthe increases in operating speed that they allow, in molding devices ofthe rotary carousel type, particularly those equipped with amultiplicity of molds, in which case the actuating means functionallyassociated with the second lock element comprise at least one idling camfollower roller supported by part of the moving part situated beyond itsbearing surface with respect to the second lock element, said rollerbeing able to collaborate with a fixed guide cam positioned laterallywith respect to the rotary carousel. Advantageously then, the actuatingmeans for actuating the second lock element comprise a return springable to return the moving part to a position for which the second lockelement is in the catching position.

Still in the case of molding devices of the carousel type, it isadvantageous, in the case of said implementation of an eccentricrotation spindle, for the means for controlling the pivoting of theeccentric spindle to comprise an idling cam follower roller supported,via a transmission mechanism, by one end of said shaft, said rollerbeing able to collaborate with a fixed guide cam positioned laterallywith respect to the rotary carousel. Advantageously then, the means forcontrolling the pivoting of the eccentric spindle comprise a returnspring able to return said spindle to its said first position.

The provisions that have just been set out may give rise to numerousembodiment variants.

In particular, it is conceivable for the first hook-shaped lock elementto be attached and fixed to the first half-mold, or alternatively, as avariant, for it to be formed as an integral part of the first half-mold.

Likewise, it is conceivable for the second hook-shaped lock element tobe attached and fixed to said moving part, or alternatively, as avariant, for it to be formed as an integral part of said moving part.

Provision may also be made for the devises that support the rotationspindle to be integral with the second half-mold or, as a variant, forsaid pivoting surface in the shape of an arc of a circle for the movingpart to be supported by a mounting plate attached and fixed to thesecond half-mold.

As indicated above, the reaction of the forces, during the blowingoperation, is distributed uniformly over the entire height of thehalf-molds. In addition, since the forces directed tangentially to themold are reacted directly and since the number of devises supporting therotation spindle is restricted to a minimum, the structures of eachhalf-mold can be lightened, this option then seeming particularlyfavorable in the case of molds with a shell/shell-holder structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from reading the detaileddescription which follows of certain preferred embodiments given purelyby way of illustration. In this description, reference is made to theattached drawings in which:

FIGS. 1A and 1B are schematic views from above, in section, of part of amold of the hinged type equipped with locking means in accordance withthe invention, shown in the locked position and in the unlocked positionrespectively;

FIG. 2 is a schematic view from above, in section, of part of a mold ofthe hinged type showing a practical embodiment variant of the lockingmeans of FIG. 1A;

FIG. 3 is a view from above of the entirety of a hinged mold equippedwith locking means according to the embodiment variant of FIG. 2;

FIG. 4 is a part view, in section and in perspective, of anotherembodiment variant of the locking means of FIG. 2;

FIG. 5 is a part view in section of an embodiment variant of part of thearrangement illustrated in FIG. 4;

FIGS. 6A, 6B and 6C are schematic views from above, in section, of partof a hinged mold showing yet another embodiment variant of the lockingmeans in three functional positions respectively;

FIG. 7 is a schematic view in perspective of the entirety of a moldarranged according to the invention; and

FIG. 8 is a schematic view in perspective of an embodiment variant ofthe mold illustrated in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

The arrangements according to the invention are improvements made tomolding devices for the blow-molding or stretch-blow-molding ofcontainers, such as bottles, from heated thermoplastic (for example PET)preforms. Such a molding device comprises at least one mold comprisingat least two half-molds (and possibly a third part that forms an axiallymovable mold bottom) which can be moved relative to one another betweenan open position in which they are parted from one another and a closedposition in which they are pressed firmly against one another bycollaborating respective faces defining a parting line, locking meansbeing provided to lock the two half-molds in the closed position andprevent them from parting or gaping when the blowing fluid is introducedunder very high pressure (for example typically of the order of 40×10⁵Pa).

Commonly, such molding devices may comprise a multiplicity of molds andmay therefore be arranged in the form of a rotary device or carouselwith the molds arranged at the periphery, the various functions ofopening/closing, locking/unlocking, etc. the molds possibly beingcontrolled in sequence as the carousel rotates by cam follower rollersborne by the molds and collaborating with guide cams mounted fixedly onthe outside of the rotary part.

Although the arrangements according to the invention can be applied toany type of mold, they are particularly applicable to molds equippedwith two half-molds that rotate one with respect to the other, or tohinged molds, which are currently in very widespread use, and it istherefore in the context of a hinged mold that the arrangements of theinvention will be set out in detail, without the protection beingrestricted to this one type of mold.

FIG. 3 illustrates, in simplified form, in a view from above, thegeneral arrangement of a hinged mold, denoted in its entirety by thereference 1, comprising two half-molds 1 a and 1 b (it also beingpossible for an axially movable bottom—not visible—to be provided at thebase of the mold). The two half-molds respectively have twocollaborating faces or bearing faces 2 a, 2 b which, in the closedposition, define a parting line 3. The collaborating faces are hollowedout with, respectively, two half-cavities 4 a, 4 b which, when puttogether, define the molding volume 4 that has the external shape of thecontainer that is to be obtained.

In the example more particularly illustrated in FIG. 3, each half-mold 1a, 1 b has a composite structure and comprises an external framework orshell-holder 5 a, 5 b and an interior molding part or shell 6 a, 6 bwhich is fixed removably into the respective shell holder and comprisessaid respective half-cavity 4 a, 4 b.

The half-molds 1 a, 1 b (in this instance the shell-holders 5 a, 5 b)comprise, on one side, respective protruding cheeks 7 a, 7 b which areinterleaved with one another in a superposed fashion and have passingthrough them a shaft 8 arranged in the continuation of the parting line.

Furthermore, two projecting lugs 9 a, 9 b respectively support inrotation, via spindles 10 a, 10 b distant from one another on each sideof the shaft 8, the ends of two actuating link rods 11 a, 11 b the othertwo respective ends of which are connected with the ability to rotatefreely on a spindle 12 which can be moved in a linear fashion (arrow 13)toward the spindle 8 or in the opposite direction, by drive means (notshown).

On the other side of the parting line 3 and on the opposite side to theshaft 8 there are locking means 14 intended to keep the two half-molds 1a, 1 b in the closed position as the blowing pressure is applied.

Referring now to FIG. 1A, the locking means 14 comprise:

-   -   a first hook-shaped lock element 15 which is secured fixedly to        the first half-mold 1 a (the left-hand one in FIG. 1A) which        extends substantially along the edge of the bearing face 2 a        thereof,    -   a second hook-shaped lock element 16, inverted with respect to        the previous one and mounted to pivot, on a rotation surface, on        the second half-mold 1 b (to the right in FIG. 1B), and    -   actuating means functionally associated with the second lock        element 16 so as to move the latter transversely to the mold        between a position of engagement with the first lock element 15        (locking the mold 1 in the closed position, as illustrated in        FIG. 1A) and a position of disengagement from the first lock        element 15 (unlocking the mold 1, as illustrated in FIG. 1B).

The first lock element 15 extends over the entire height of the firsthalf-mold 1 a and the second lock element 16 extends over the entireheight of the second half-mold 1 b.

The second half-mold 1 b comprises, along the edge of its bearing face 2b and over at least most of its height, a radially projecting flange 17shaped, on its face facing away from the bearing face 2 b, as an arc ofa circle and able to constitute said rotation surface 18 (which isconvex in FIGS. 1A and 1B) for the second lock element 16.

This being the case, the second lock element 16 belongs to a moving part19 which extends over the entire height of the second half-mold 1 b. Oneof the edges of this moving part 19 forms the second hook-shaped lockelement 16, while its opposite edge is provided with a transverseprojecting flange 20 defining a bearing surface in the shape of an arcof a circle 21 (concave in FIGS. 1A and 1B) which faces toward thesecond lock element 16 and is able to bear over the entire height ofsaid rotation surface 18.

By virtue of this arrangement, the two half-molds 1 a, 1 b are kept inthe closed position by the moving part 19 the two opposite edges (secondlock element 16 and flange 20) of which are engaged againstcomplementary parts of the first half-mold 1 a (first lock element 15)and of the second half-mold 1 b (projecting flange 17). Furthermore, thetwo half-molds 1 a, 1 b are held in the closed position over the entireheight of the mold substantially continuously, rather thandiscontinuously as was the case with the locking means involving movingfingers used hitherto.

Producing the bearing surface in the shape of an arc of a circle 18 mayprove difficult and expensive to achieve, and one concrete exemplaryembodiment which is simpler and more economical to manufacture isillustrated in FIG. 2. Here, the projecting flange 17 has its facefacing away from the bearing face 2 b hollowed out by a groove 22 in theshape of an arc of a circle extending over the entire height thereof anda spindle 23 is engaged in said groove. Said rotation surface 18 here isa convex surface consisting of the surface of the spindle 23. In such acase, in the locked position illustrated in FIG. 2, the forces that tendto part the two half-molds 1 a, 1 b from one another during blowing arereacted by the moving part 19, via, on the side of the second half-mold1 b, the rotation spindle 23. By giving the grooves 21 of the movingpart 19 and 22 of the flange 17 of the second half-mold 1 b perfectlymatched shapes that complement the external surface of the spindle 23,perfect reaction of the forces over the entire height of the mold isguaranteed, with lower pressures on the contact surfaces. It is thenpossible to produce parts that are less massive and therefore lessheavy, which therefore have lower inertias; what is more, the angularexcursion of the moving part 19 between the locked and unlockedpositions is small, and the shorter travel of this part, which manifestsitself in a shorter transit time, contributes to permitting an increasein operating rates.

To control the movement of the moving part 19 it is possible, asillustrated in FIG. 3, to provide at the base of the moving part anextension 24 thereof the end of which supports a cam follower roller 25that idles freely. Since the mold 1 belongs to a molding device of thecarousel type, the roller 25, as the device rotates, may come intocontact with a guide cam (not shown) mounted fixedly and laterally withrespect to the rotating part. It is thus possible selectively to controlthe movement of the moving part 19. To simplify the set-up of thesecontrol means, it is possible to envisage for them to comprise a spring26 associated with the extension 24 of the moving part 19 and able toreturn the latter to a position knocked down toward the mold: thus, themoving part 19 is kept in a position such that, as the two half-moldsapproach one another, the moving part 19 engages on the first lockelement 15 automatically: locking is therefore obtained automaticallyand ensured. The interaction between the follower roller 25 and theguide cam then occurs only to bring about the disengagement of themoving part 19 from the first lock element 15 with a view to opening themold.

In the examples illustrated schematically in FIGS. 1A, 1B, 2 and 3, thefirst lock element 15 is shown as forming an integral part of the firsthalf-mold 1 a, particularly as forming an integral part of the firstshell-holder 5 a.

It is of course possible, as a variant, to envisage for the first lockelement 15 to belong to the part attached to the first half-mold, forexample in the form of a plate 27 bolted to the first half-mold 1 a,particularly the first shell-holder 5 a, as illustrated in FIG. 4 (whichFIG. 4 illustrates, in section, another configuration of hinged moldwith semi-rectangular shell-holders 5 a, 5 b—the shells not being shownin order to make the drawing easier to understand).

Likewise, the transverse flange 17 too may belong to a part attached tothe second half-mold 1 b or the second shell-holder 5 b, for example inthe form of a plate 28 bolted to the second half-mold 1 b or to thesecond shell-holder 5 b, as illustrated in FIG. 4.

The arrangements proposed with reference to FIG. 4 allow the structureand therefore the manufacture of the first and/or second half-mold or ofthe first and/or second shell-holder to be simplified. Furthermore, itis possible to make one and/or the other of the lock elements 15, 16from different metals from the corresponding half-mold or shell-holder,particularly when these are aluminum castings (it then being possiblefor the lock elements to be made of steel).

To retain the spindle 23, provision may be made for the second half-mold1 b or the second shell-holder 5 b, or alternatively still, said plate28, to comprise a small number of hollowed-out projecting devises 29through which the spindle 23 passes. Advantageously, just two devises 29may be provided, these being located near the respective ends of thespindle 23 (the bottom clevis 29 is visible in FIG. 4). Likewise, thelower and upper parts of the moving part 19 are arranged like a devise30 accommodating the ends of the spindle 23. Because the forces arereacted transversely by the bearing parts on either side of the spindle23, the devises 29, 30 do not have to transmit any force and their solefunction is to retain the spindle outside of the blowing periods: thespindle does not therefore have to be fitted with excessively closetolerances and the devises can be sized as small as possible in order toleave the spindle clear over a maximum height so as to increase thebearing length.

This bearing length can be increased still further by arranging theupper and lower ends of the spindle 23 in cups provided on the movingpart 19. For example, as illustrated in FIG. 5, the lower part 30 of themoving part 19 may be positioned under the lower face of the plate 28 sothat the clevis 29 lies flush with this lower face. This lower part 30is hollowed out to form a cup 31 accommodating the lower end of thespindle 23. The upper part 32 of the moving part is bored and the upperend of the spindle 23 passes through it. It may possibly be capped by acover plate 33 protecting the end of the spindle.

FIGS. 6A to 6C illustrate an embodiment variant that is highlyadvantageous because it allows locking to be confirmed. The arrangementis identical to the one illustrated in FIG. 2 except that the spindle 23is an eccentric pivoting spindle.

In the unlocked position illustrated in FIG. 6A, the spindle 23 isoriented angularly with its smallest-radius portion in contact with thegroove 21 of the moving part 19.

Next, the moving part 19 is pivoted about the spindle 23 to engage inthe hook-shaped lock element 15 in order to lock the two half-molds 1 a,1 b in the closed position (FIG. 6B).

Finally, the spindle 23 is rotated on itself so that the radius of theportion engaged in the groove 21 increases, and this has the effect ofpushing the moving part 19 to the right (in FIG. 6C) and therefore offorcing the second lock element 16 against the first lock element 15 ofthe first half-mold 1 a. Simple confirmation of the locking is thusobtained.

Upon unlocking, rotating the spindle 23 in the opposite directionreleases the second lock element 16 from the first lock element 15 whichis fixed and the outward pivoting of the moving part 19 can then beperformed.

The rotation of the spindle 23 may for example be obtained (FIG. 7) byrigidly associating with it, at one of its ends, an arm 34 supporting,at its free end, an idling cam follower roller 35 which is able tocollaborate with a guide cam positioned, fixedly, laterally with respectto the rotary part of a molding device of the carousel type.

FIG. 7 schematically illustrates in perspective the essential elementsof a mold 1 arranged according to the invention as illustrated in FIGS.6A to 6C, the mold 1 here being visible over its entire height.

By virtue of the arrangements employed in accordance with the invention,the forces to which the shell-holders 5 a, 5 b are subjected are lowerthan in the earlier arrangements, particularly because of a lower massand a lower inertia. This being the case, it is possible, in conjunctionwith a shorter angular excursion of the moving part 19 of the lockingmeans, to envisage increasing the production rate of the mold.

Still with a view to lightening the moving parts and to reducing inertiain order to allow production rates to be increased, it is also possibleto envisage forming the first lock element 15 and/or the second lockelement 16 in the form of parts extending discontinuously over theentire height of the half-molds 1 a, 1 b, as illustrated in FIG. 8. Inthe example illustrated in FIG. 8, it has been assumed that the two lockelements 15 and 16 were produced in the form of a multiplicity of hooks38, 39 respectively, discontinuous, positioned facing each other andable to engage in pairs. If the number of these pairs of hooks 38, 39 ishigh enough, in other words if the spacings 40 between the hooks are nottoo great (for example it is possible to anticipate spacings 40 havingapproximately the same height as the hooks 38, 39), then an appreciablyuniform reaction of force is obtained, similar to that afforded bycontinuous hook-type lock elements as illustrated in FIG. 7. To give aconcrete example, the number of these hooks 38, 39 may be of the orderof about ten distributed over a height of the order of 35 cm (a mold fora 1.5-liter bottle for example).

As a variant, it is possible to envisage associating a continuous hooklock element (for example the first lock element 15 which is fixed) anda multiple-hook lock element (particularly the second lock element 16which is the moving one).

1. A molding device for blow-molding or stretch-blow-molding containersfrom heated thermoplastic preforms, said device comprising at least onemold comprising at least two half-molds that can be moved with respectto each other between an open position in which they are parted from oneanother and a closed position in which they are firmly pressed againstone another via collaborating respective bearing faces defining aparting line, locking means being provided to lock the two half-molds inthe closed position, which locking means comprising on at least one sideof the mold, a first lock element in the form of a hook secured fixedlyto the first half-mold along the edge of the bearing face thereof, asecond lock element in the form of a hook inverted with respect to theprevious one and mounted such that it can pivot, on a rotation surface,on the second half-mold, and actuating means functionally associatedwith said second lock element in such a way as to move the lattertransversely between a locked position in which it is engaged with thefirst lock element to lock the two half-molds in the closed position andan unlocked position in which it is disengaged from the first lockelement to release the two half-molds that can then be parted from oneanother, wherein, in addition: the first and second hook-shaped lockelements extend respectively over the entire height of the first andsecond half-molds, the second half-mold has, along the edge of itsbearing face and over at least most of its height, a radially projectingflange shaped, on its face facing away from the bearing face, as an arcof a circle and able to constitute a rotation surface, and said secondlock element belongs to one end of a moving part provided with atransverse projecting flange defining a bearing surface in the shape ofan arc of a circle facing toward the second hook-shaped lock element andable to bear continuously over the entire height of said rotationsurface of the second lock element, whereby, when the mold is closed andlocked and subjected to the blowing pressure, the force to which thesecond half-mold is subjected is reacted, by said moving part,substantially continuously over most of its height via said rotationsurface.
 2. The molding device as claimed in claim 1, in which the moldis of the hinged type with the two half-molds articulated to one anotherin terms of rotation on a shaft substantially parallel to one side ofthe parting line, wherein said locking means are provided on theopposite side of the two half-molds to said shaft.
 3. The molding deviceas claimed in claim 1, in which each half-mold comprises a shell holderto which there is internally fixed a shell equipped with a moldinghalf-cavity the parting line being defined by the two shells pressedtogether when the mold is in the closed position, wherein the lockingmeans are supported by the two shell-holders.
 4. The molding device asclaimed in claim 1, wherein said face of the protruding flange of thesecond half-mold which faces away from the edge of the bearing face ishollowed out in the shape of an arc of a circle and houses a rotationspindle the free surface of which constitutes said rotation surface. 5.The molding device as claimed in claim 4, wherein the rotation spindleof the moving part supporting the second lock element is supported by asmall number of hollowed-out devises secured to the second half-mold. 6.The molding device as claimed in claim 5, wherein the devises are two innumber, distant from one another and, in particular, situated near therespective ends of the spindle.
 7. The molding device as claimed inclaim 4, wherein the rotation spindle of the moving part supporting thesecond lock element has a height appreciably greater than that of thesecond lock element and in that its two ends are engaged in tworespective cups, secured to the second mold, whereby the moving partsupporting the second lock element bears over substantially the entiretyof its height against the rotation spindle.
 8. The molding device asclaimed in claim 1, wherein the first and second hook-shaped lockelements extend continuously over their entire height.
 9. The moldingdevice as claimed in claim 1, wherein at least the second hook-shapedlock element extends discontinuously over its entire height andcomprises a multiplicity of hooks separated from one another anddistributed over its entire height.
 10. The molding device as claimed inclaim 4, wherein the rotation spindle is arranged in the form of aneccentric spindle and in that pivot control means are associated withit, whereby the spindle is able to occupy two angular positions withrespect to the moving part, namely a position at minimum radius forwhich the moving part bears against the part of the spindle that has aminimum radius and for which the moving part can be made to move towardits locked position or toward its unlocked position and a position at agreater radius for which the moving part bears against a part of thespindle that has a radius greater than the minimum radius and for whichthe moving part, in the locked position, is immobilized in this positionbeing subjected to traction between the first and secondmutually-engaged lock elements and the rotation spindle.
 11. The moldingdevice as claimed in claim 1, this device being of the rotary carouseltype, wherein the actuating means functionally associated with thesecond lock element comprise at least one idling cam follower rollersupported by part of the moving part situated beyond its bearing surfacewith respect to the second lock element, said roller being able tocollaborate with a fixed guide cam positioned laterally with respect tothe rotary carousel.
 12. The molding device as claimed in claim 11,wherein the actuating means for actuating the second lock elementcomprise a return spring able to return the moving part to a positionfor which the second lock element is in the catching position.
 13. Themolding device as claimed in claim 10, this device being of the rotarycarousel type, wherein the means for controlling the pivoting of theeccentric spindle comprise an idling cam follower roller supported, viaa transmission mechanism, by one end of said shaft, said roller beingable to collaborate with a fixed guide cam positioned laterally withrespect to the rotary carousel.
 14. The molding device as claimed inclaim 10, this device being of the rotary carousel type, wherein themeans for controlling the pivoting of the eccentric spindle comprise anidling cam follower roller supported, via a transmission mechanism, byone end of said shaft, said roller being able to collaborate with afixed guide cam positioned laterally with respect to the rotarycarousel, and in that the means for controlling the pivoting of theeccentric spindle comprise a return spring able to return said spindleto its position of minimum radius.
 15. The molding device as claimed inclaim 1, wherein that the first hook-shaped lock element is attached andfixed to the first half-mold.
 16. The molding device as claimed in claim1, wherein the first hook-shaped lock element is formed as an integralpart of the first half-mold.
 17. The molding device as claimed in claim1, wherein the second hook-shaped lock element is attached and fixed tosaid moving part.
 18. The molding device as claimed in claim 1, whereinthe second hook-shaped lock element is formed as an integral part ofsaid moving part.
 19. The molding device as claimed in claim 1, whereinsaid pivoting surface in the shape of an arc of a circle for the movingpart is supported by a mounting plate attached and fixed to the secondhalf-mold.